1. Technical Field of the Invention
In general, the present invention relates to machining of a workpiece. More particularly, the present invention relates to end-mill tools for milling a workpiece and a related method.
2. Background of the Invention
Rotary cutting end-mill tools are used for various machining operations on workpieces. Such machine operations are generically referred to as milling operations and include the forming of slots, keyways, pockets, and the like. Several considerations related to end-mill tool design include time for completing a machining operation, amount of material removed in a cut, quality of the cut, and wear on the tool itself during the milling operation.
The various machining operations performed with an end-mill tool can be performed in a "roughing" mode (rough cutting) and a "finishing" mode (finishing cutting). During roughing, material is removed from a workpiece at a relatively high rate (e.g., depth of cut), but with a relatively rough surface finish. Finishing involves the removal of material from a workpiece at a relatively low rate, but with a relatively smooth surface finish. Generally, these two operations (roughing and finishing) are antithetical to one another, and require two operations with two different end-mills.
End-mill tools are formed from materials such as tungsten carbide, high speed steel, ceramic, and other advanced materials and coatings and typically include a "shank" portion, a "body" portion and a "point". The shank portion is located towards one end of the end-mill tool and is generally cylindrical (but may be tapered) for engagement by a spindle of a milling machine. In use, the milling machine rotatably drives the end-mill tool about its longitudinal axis. The body portion of the end-mill tool is located between the shank and the point. The point is formed at an opposite end of the tool from the shank portion, and typically includes one or more cutting edges.
To manufacture an end-mill tool, a grinder is typically used to grind a flute face and a corresponding cutting edge on the body of the end-mill tool. The grind (grinding operation) typically starts from a position adjacent an end of the body portion and continues to a point at or near the interface of the body portion and the shank portion, commonly referred to as an "inception location". The grind forms a desired helical flute face and/or helical cutting edge. Prior art end-mills typically have continuous helical flutes with continuous cutting edges helically extending from the inception location to the point (or vice-versa). The flutes function primarily for chip removal, in a manner similar to the helical flutes found on an ordinary drill bit.
An end-mill tool representative of the end-mill tools of the prior art is illustrated in FIGS. 1A and 1B and identified with reference numeral 100. The tool 100 has been formed of cylindrical rod stock which has been ground to form distinctive portions. At one end of the tool 100 is a shank portion 102, suitable for chucking to the spindle of a milling machine (not shown) for rotating and advancing the tool 100. At an other end of the tool 100 is a point 104 which is provided with flat cutting edges 114 and 116. Between the shank portion 102 and the point 104 is a body portion 106 which is helically ground to have a number of flutes 110 and 112. A "boundary" between the body portion 106 and the shank portion 102 is designated 108 in the drawing.
In the embodiment illustrated, the formation of flutes in the body portion 106 generally involves the grinding of two channels, or flutes 110 and 112, which form two diametrically-opposed positions at the point 104 towards the shank portion 102. The grinding is discontinued at the boundary 108 of the body portion 106 and the shank portion 102. It will be appreciated that the direction of the grind could, of course, be reversed. In a known variation referred to as a three-flute end-mill, three flutes wind helically around the body portion of the tool and terminating in three cutting edges. The flutes 110 and 112 are formed at a helix angle which "winds" around the cylindrical body portion.
Generally, the location of the flat cutting edges 114 and 116 is determined by the location of the flutes 110 and 112 at the point 104 of the tool 100. The end-mill tool 100 illustrated in FIG. 1A has two cutting edges 114 and 116 at the point 104. The number and location of the cutting edges 114 and 116 is determined by the flutes 110 and 112. FIG. 1B shows the cutting edges 114 and 116 of the tool 100 in greater detail.
It is known in the art to form flutes at a low helix angle or a high helix angle. A "low helix" (or low helical flute) is a flute that helically "winds" around a cylinder at an angle of no more than 45.degree. (forty-five degrees). A "super" low-helical flute would be a flute that winds around a cylinder at an angle of at no more than 15.degree.. A "high helix" (or high helical flute) is a flute that helically winds around a cylinder at an angle of greater than 45.degree.. A "super" high-helical flute would be a flute that winds around a cylinder at an angle of at least 65.degree.. Low helix angle flutes are typically employed for rough cutting while high helix angle flutes are employed for finish cutting.
Returning to FIG. 1A, the tool 100 is illustrated to include two cutting edges 120 and 122. Each of the cutting edges 120 and 122 is helical and follows one of the flutes 110 and 112 helically around the body portion 106. A notable feature of these cutting edges 120 and 122 is that they are "continuous"--in other words they helically extend continuously from the point 104 to the shank 102. These cutting edges 120 and 122 function to remove material in the linear direction of travel of the end-mill 100 (e.g., from right-to-left, as viewed in FIG. 1A) during a machining operation when the end-mill is "buried" into a workpiece. Material removed from the workpiece will tend to be in the form of an elongated helical (curlicue) chip, and will be guided away from the workpiece by the channels formed by the flutes 110 and 112.
By way of further definition, the edges 114 and 116 at the point 104 of the tool 100 can be considered to be "flat" cutting edges, and the cutting edges 120 and 122 along the body 106 of the tool 100 can be considered to be "helical" cutting edges.
The following U.S. Patents are further instructive of the prior art: U.S. Pat. Nos. 4,610,581; 5,049,009; 4,721,421; and 4,963,059. These patents are incorporated by reference as if fully set forth herein.
Numerous variations of the grind (e.g., flute angle) have been attempted for end-mill tool design. Prior advancements relating to material removal and feed rate of end-mill cutters have been accomplished by (1) varying the spiral lead angle; (2) increasing the depth of the flutes in the body portion of the end-mill, (3) changing the radial rake; (4) changing the clearance angles of the cutting edges; and (5) forming chip splitting grooves in the flutes.
While such variations have proven successful in various applications, they are also associated with disadvantages and limitations. For example, such variations may weaken the core diameter of the end-mill cutter, thereby weakening the tool. Additionally, such noted variations are not suitable for a particular applications (e.g., regarding milling time, rough cut, finish cut, etc.). Furthermore, known end-mills are not efficient for both rough cutting and finish cutting.
It is often advantageous when performing an end-mill machining operation to create many small chips, rather than fewer elongated curlicue chips. This allows, for example, rapid rate of removal of material from a workpiece without undue heating of the end-mill tool. Heat is generally anathema to tools, particularly end-mill tools. To the end of reducing heat, it is known to use coolants. Dry machining (sans coolant) offers an advantage of simplicity. Generally, the end-mill of the present invention provides for increased rate of removal without sacrificing tool life and strength, and may not require flowing coolant onto the workpiece or tool.